Effect of plant growth on the distribution and forms of soil nutrients in the rhizosphere

Abstract

The effect of plant growth on the distribution and forms of soil nutrients in the rhizosphere was studied by growing plants in rhizoboxes. An experiment was carried out in a growth chamber for 17 d with three treatments, i.e. maize (Zea mays L.), kidney bean (Phaseolus vulgaris L.), and no plants. After the experiment, soil samples were collected up to about 50 mm from the central compartment (C. C.) in which roots were allowed to grow, and analyzed for the soluble, exchangeable, and total amounts of nutrients. Plant samples were also analyzed for their nutrient contents.

The pattern of nutrient distribution in the rhizosphere varied among the types and forms of elements. In both maize and kidney bean, the concentrations of soluble P, K, and N decreased significantly at the C.C., up to 4 mm and up to 10 mm from the C.C., respectively. The magnitude of their depletion reflected their rate of diffusion in soil. The concentration of exchangeable K decreased significantly up to 2 mm from theC.C., whereas those of exchangeable Ca and Mg increased within 1 mm from the C.C. The total amount of nutrients, however, did not change significantly for each element. The depletion of soluble P and K mainly around the C.C. indicated the presence of their diffusion toward the root surface. Their uptake was larger than the apparent decrease of their soluble forms, suggesting that their depletion was compensated by intensive replenishment from the soil solid phase. The concentrations of N, Ca, and Mg, on the other hand, markedly decreased up to the end of the rhizobox, indicating the presence of mass flow. The depletion was proportional to the rate of transpiration by plants.

Key Words:

• diffusion
• mass flow
• nutrient depletion
• replenishment
• rhizosphere